FIG. 25 is a diagram illustrating the structure of a network monitoring control system disclosed in WO 2002/045352 A. In FIG. 25, reference numeral 10 denotes a monitor apparatus, reference numeral 11 denotes a gateway server, and reference numerals 12 to 15 denote transmission apparatuses which are connected to form a ring network by an optical cable 23. Each of the transmission apparatuses 12 to 15 communicates monitor control information with each other in the ring network.
The monitor control information is transmitted as SDH header information elements D1, D2, and D3 of an SDH optical signal which is transmitted through the optical cable 23. In FIG. 25, the DCC channel 24 represented by a dotted line transmits the monitoring control information between the transmission apparatuses. The “DCC” is an abbreviation of a data communication channel.
The monitor apparatus 10 is physically connected to a specific transmission apparatus (GNE) among the transmission apparatuses 12 to 15 through the gateway server (GWS) 11 in order to perform a monitor and control on the ring network. The monitor apparatus performs communication for the monitor control information based on a predetermined communication protocol. The “GNE” is an abbreviation of a gateway network equipment or a gateway network element.
In FIG. 25, physical links 21 and 22 are formed by using separate cables between the gateway server 11 and a plurality of GNEs (for example, two GNEs 12 and 13).
The first GNE 12 and the second GNE 13 are designed and set by a maintainer. Thereafter, the gateway server 11 controls the link 21 and the link 22 according to, for example, the load state of the GNEs 12 and 13 to achieve an autonomous distributed process.
In the system disclosed in WO 2002/045352 A, it is possible to control the switching or operation of the two GNEs which are set in the ring network in advance. However, when a failure (for example, a double failure) occurs in each of the transmission apparatuses set as the GNEs, a GNE function is no longer available in the ring network.
When a load is concentrated on all of the transmission apparatuses set as the GNEs, it is predicted that the GNE function will be impaired even though the load is distributed, similarly to the case of the double failure.
Further, since the maintainer intervenes in the design and setting operation to build the GNE, a human error may be occurred.